The mother of NZ First MP Brendan Horan spent money on operations and a new car in the years before she died, a close family source says.

Mr Horan was absent from Parliament yesterday after being told by party leader Winston Peters to sort out claims raised by his half-brother Mana Ormsby about money going missing from the bank account of his late mother.

Forensic accountants have been asked to investigate his mother's estate, amid allegations that large sums of money were misappropriated from her bank accounts over several years.

Mr Horan has welcomed the investigation, saying he wanted to clear up allegations.

Mr Peters would not say how long Mr Horan would be away from Parliament. Mr Horan's "No 1 priority" was to sort out the family matter, he said.

Olwen Horan was 87 when she died in August with less than $3000 in her current account, down from $259,000 in February 2007. The Mt Maunganui resident won about $1 million in prizes in an Australian lottery in 1999.

Mr Horan's other brother, Peter Horan, has said he also had concerns that money was missing.

A family source said yesterday Mrs Horan "spent like a trooper" in the years before she died.

She bought a new Mazda 6 and spent money on operations and plastic surgery in an attempt to save her failing eyesight and her nose after she was diagnosed with skin cancer, the source said.

In July, Mrs Horan signed a codicil, or amendment, to her will, stating that the executor of the estate, her nephew John Buckthought, be authorised to recover money from Mr Horan and his sister, Marilyn Bleackley, "loaned to them by me or taken from me by misadventure".

Mr Peters twice yesterday refused to express confidence in his MP and reiterated he was still waiting for facts from the family on allegations he described as "very serious".

Mr Horan refused to comment yesterday, saying he was taking legal action. "The lawyers are working on it and things are moving along pretty quickly."

Mrs Horan's will states her house was to be sold, with the first $150,000 going to Peter Horan, who had been declared bankrupt, and the rest divided between her other children. The house sold recently for $425,000.

Mrs Bleackley said yesterday that she had power of attorney for her mother's estate for 10 days.